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In vivo selection for transmissible drug resistance in Salmonella typhi during antimicrobial therapy
R S Schwalbe1, C W Hoge, J G Morris
1Department of Pathology, University of Maryland School of Medicine, Baltimore 21201.
Abstract:
We report the recovery of Salmonella typhi that acquired resistance to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and gentamicin subsequent to multiple antibiotic therapy. Escherichia coli and Klebsiella pneumoniae isolates which were recovered from the same stool sample displayed identical resistance patterns. Agarose gel electrophoresis revealed that S. typhi and laboratory-derived transconjugants contained a high-molecular-weight plasmid present in the resistant intestinal bacteria.
Insights
Salmonella typhi developed resistance to multiple antibiotics after treatment. Identical resistance patterns were observed in co-occurring Escherichia coli and Klebsiella pneumoniae, linked by a shared plasmid.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Antibiotic resistance is a growing global health threat.
- Multidrug-resistant bacteria pose significant challenges in clinical settings.
- Salmonella typhi is a major cause of enteric fever worldwide.
Purpose of the Study:
- To investigate the emergence of multidrug resistance in Salmonella typhi.
- To identify the genetic basis for acquired antibiotic resistance.
- To examine the relationship between resistant bacterial isolates from the same source.
Main Methods:
- Bacterial isolation and identification from stool samples.
- Antimicrobial susceptibility testing for multiple antibiotics.
- Agarose gel electrophoresis to analyze plasmid DNA.
Main Results:
- Salmonella typhi acquired resistance to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and gentamicin.
- Escherichia coli and Klebsiella pneumoniae isolates exhibited identical resistance profiles.
- A high-molecular-weight plasmid was identified in S. typhi and transconjugants, present in other resistant bacteria.
Conclusions:
- Multiple antibiotic therapy can drive the acquisition of resistance in Salmonella typhi.
- Plasmid-mediated horizontal gene transfer likely contributed to the spread of resistance.
- Co-infection with other resistant Enterobacteriaceae may facilitate resistance development.